112 MORPHOLOGY OF THE ANGIOSPERMS 



The connective cannot be delimited: proximally, it often merges with 

 the filament (Fig. 49C, D, F, H, 7, L); laterally, it consists of the 

 reduced and contracted laminar tissues of the ancestral sporophyll 

 which sheathe the sporangia. In the older literature, the connective was 

 called "placental," because of analogy, or supposed homology, with the 

 ovule-bearing structure. The suggestion that "connective" be applied 

 only to "conventional types" of stamens, and "sterile tissue" replace it in 

 others is not acceptable, because no line can be drawn between "con- 

 ventional" stamens and other forms, and because sterile tissue is not 

 limited to the connective but sheathes the entire anther. 



The distal appendage of the connective (Fig. 49B, F, /, K), a typical 

 feature of the anther in more or less primitive families — Magnoliaceae, 

 Nymphaeaceae (Fig. 54B, C, D, G, J, M), Cercidiphyllaceae (Fig. 146), 

 Eupteleaceae — is largely lost in advanced families, though it may persist 

 there and even be elaborated. In the Magnoliaceae and some other 

 families of the woody Ranales (Figs. 50 and 51), it is a prominent 

 feature of flower structure. It occurs also scattered throughout the angio- 

 sperms — even in so advanced a family as the Compositae, where it un- 

 doubtedly represents elaboration of anther form related to pollination 

 methods, rather than the persistence of a primitive character. 



Early stages in the specialization of the anther are seen in stamens 

 where the connective is prominent and anther and filament merge ( Figs. 

 49B, C, D, F, I, L; 50; and 51) and where filaments are "flattened," 

 often with narrow wings and sporangia somewhat decurrent on the 

 filament (Fig. 49D, F, I, L). In cross section, the anther is frequently 

 symmetrically four-sided, with a sporangium in each corner. Transitional 

 forms between this and the advanced stamen, with sharply set-off 

 anther and slender, terete filament, are common. Anther structure is 

 usually constant throughout a genus and often throughout a family. 



The Filament 



The filament ranges in form from broad and winged to terete and 

 threadlike, and from short to long. The broader and shorter types are, 

 in general, the more primitive. Sessile anthers occur occasionally — 

 Juglans. Absence of the filament may be the result of reduction in 

 adaptation to special habitats or methods of pollination, as in many 

 aquatic genera — Najas, Zostera — or the result of adnation of the fila- 

 ment to the perianth, where the filament is absent superficially, though 

 not lost morphologically, and is often represented by its vascular supply 

 — some of the Proteaceae and Loranthaceae. Some primitive stamens 

 with sporangia near the base and no distinction of filament (Fig. 49jE, 

 F, G, I) have also been described as sessile — Himantandra (Fig. 50). 



